Final answer:
The sectionalized aria form of the early 19th century Italian opera is known as Bel canto, which emphasizes beautiful, melodic singing with technical skill and was prominent in works by composers like Bellini, Donizetti, and Rossini.
Step-by-step explanation:
The sectionalized aria form of the early 19th century Italian opera is best described as Bel canto. This term literally means 'beautiful singing' in Italian, and it is characterized by a focus on the purity of vocal tone and the virtuosic agility of the singers. Bel canto opera emphasizes melodic lines and requires a high level of technical proficiency from the vocalists. During this period, the use of arias in opera was critical for showcasing a singer's vocal abilities through ornamented, lyrical melodies. This style flourished in early 19th century Italian opera, where composers like Bellini, Donizetti, and Rossini wrote works that required singers to perform with dynamic expression and technical skill. Therefore, the answer to the question is 4) Bel canto.